Ok I'm mid cook and I determined its a thermometer placement issue. I added a 4" od stack I made with some .032 aluminum I had at work. Now I have 4 ea 3/4" ball valve inlets plus two more 1-1/8" holes with a sheet metal damper.
Didn't have time to to buy a better thermometer by today but the one I'm using is pretty accurate. Its the placement on the door that's the problem. It's reading about 170, but I put the meat thermometer which is also accurate (tested in boiling water) inside on a grate with the probe not touching any metal, and it's maxed out at 200. So I'm somewhere above that I think.
I'll keep you updated on the progress.